also, if you call your Block Flow with parameters id=123&folderId=456&path=path then these parameters will be automatically mapped to the inputs with the same name which are set in the flowScope. So you won't need these set elements in you <on-start> anymore.

also FYI you can use <input name="visibility" type="java.util.ArrayList"/> and <input name="tree" value="folderBean.treeAsMap"/> and get rid of your <on-start> completely.